No one knows why they exist, but theories range from serial killers to fertility rituals.

Humans have a natural desire to leave their mark on the world, as either an expression of ego or simple mischievousness.

Most of the time, these markings are pretty ordinary — crass messages written in Sharpie on bathroom stalls, for example, or spray-painted tags on highway underpasses.

But sometimes, the inscrutable symbols and signs that people leave in public places are oddly beautiful. Consider the locks people put on that bridge in Paris, for instance, or the decades’ worth of messages visitors have written to Elvis on the gates of Graceland.

A stranger manifestation of this singular human desire are “shoe trees” — trees in seemingly random places that are festooned with sneakers, boots, slippers, sandals, ice skates and other kinds of footwear.

Unlike the Love Locks bridge in Paris or the gates of Graceland, though, shoe trees exist in hundreds of places, all around the world, and anybody can start one.

But their origin story is much more interesting and complex.

The phenomenon began in North America — at least as far back as the Great Depression, when people living in the same community sometimes hung extra pairs of shoes on trees for others to take, since not everyone could afford to have their own pair.

Woodstock, Illinois. | via Waymarking.com

When the Depression ended, the tradition continued. America became embroiled in a series of wars — first World War II, then the invasions of Korea and Vietnam — and soldiers returning home from battlefields abroad started tying their military boots together and tossing them into trees as a way of saying, “I’m done; time for a new chapter.”

This unusual custom somehow, at some point, spilled out of North America and onto other continents. But no one seems to know how or when or why.

A 60-year-old shoe tree in northeast Idaho that mysteriously burned down in 2010. | via sondahl.com

According to hundreds of users’ photos posted on Waymarking.com, a public platform where people record and categorize unique locations around the world, there are shoe trees in Hawaii, Australia, Germany, the Netherlands, the United Kingdom, South Africa and beyond.

If you read other languages besides English, you’ll find evidence of shoe trees in China, Russia, the Middle East and virtually every other corner of this vast planet.

Some people make spectacular claims: The legend around a shoe tree in Salem, Michigan, for example, holds that a local serial killer nailed his victims’ shoes to the tree trunk to keep a tally of how many lives he’d taken.

Meanwhile, one writer for The Toronto Sun reported that, in Europe and the U.K., shoe trees are “some kind of fertility ritual.” Somewhat maddeningly, he doesn’t say what the ritual is, or what slinging shoes into tree branches has to do with sex.

If you scour the internet for long enough, you’ll also find anecdotes of people who’ve thrown the shoes of a dead loved one high into a nearby tree, as a kind of memorial.

A shoe tree near Salem Michigan that people claim was started by a local serial killer. | via MichiganOtherSide.com

“One young lady, her father passed away, she threw his shoes up there,” the mayor of a small town in rural Ontario told a local news outlet in 2016. “[Sometimes] she stops and visits and talks to him.”

Some people write messages or personal accomplishments on their shoes, usually in permanent marker, before hurling them into that huge elm or oak tree near that bend in the road behind the old train station. Or whatever.

In some places, legend holds that if you cause a pair of shoes to fall off the tree, it’s bad luck for life.

The common denominator among all these theories is probably a little less exciting: The trees exist because people enjoy throwing their shoes… into trees.

It’s “just a quirky little local tradition,” said Kristin Connon, a writer who lives near a shoe tree in “Smalltown, USA,” in a comment on a recent Bored Panda article about shoe trees. A writer for Roadside America, which chronicles “offbeat” destinations, says shoe trees are nothing more than “a strange ritual by bored locals.”

But does the reason for shoe trees have to be majestic for the result to be majestic — which it clearly is to so many people? After all, if the goal of lobbing your old footwear into a tree is to “leave your mark,” it’s working.

A lot of these shoe trees have been around longer than the houses next to them. They’re “handed down from generation to generation,” said a writer for The Record, a newspaper in Canada’s Waterloo Region.

Sure, the trees will eventually die. They’ll get torn out of the ground by high winds, like the giant shoe tree in Beaver, Arkansas that was the victim of a storm 18 years ago. Or they’ll be knocked over by bulldozers, or burned down, bubbling into a “molten rubber fire,” like the tree in Priest Lake, Idaho, where firemen found shoes dating as far back as the 1940s after the tree was mysteriously torched in 2010.

Does it matter if the trees rot, wither and disintegrate?

Maybe not. More will sprout in their place, and us mortals, whose lives are, after all, just a brief flicker in the span of eternity, will continue to document and photograph them so that future generations will receive a piece of our cultural history, however small, however weird it may be.

I'm a 34-year-old writer in Chicago, working as a Senior Editor at Dose, a digital media agency and publisher.
Before joining Dose, I spent 1.5 years freelance reporting from Jerusalem, where I covered conflict and culture for Vice, Al Jazeera English and others.
From 2010-2015, I was a staff editor and reporter at The Huffington Post in New York.